First-principles study of C chemisorption and diffusion on the surface and in the subsurfaces of Ni(1 1 1) during the growth of carbon nanofibers

Abstract

First-principles calculations based on density functional theory and the generalized gradient approximation have been used to study the C chemisorption and diffusion on the surface and in the subsurfaces of Ni(1 1 1). The threefold Hcp site is observed to be preferred by the C adsorption on Ni(1 1 1) surface while in the subsurfaces, the octahedral site is more energetically favorable than the tetrahedral site and all surface adsorption sites. The calculated binding energies have been compared with the previous experimental and theoretical results and good agreement is found. Minimum energy paths for the C diffusion between different adsorption sites are also investigated using the nudged elastic band method. It is predicted that if the C surface diffusion rate is higher than the production rate of C atoms during the growth of carbon nanofibers and the C concentration is low at the Ni surface, the generated C atoms are likely to diffuse on the catalyst surface predominantly because of the lowest energy barrier, while if the generated C production rate is higher and some adsorption sites are blocked by the accumulated carbon, the C atoms may diffuse both on the surface and in the subsurfaces simultaneously.